For me there is something about the world. Every level is an island in an ocean of nothing it seems like, with an eternal flat sky above it. They may not of intended it that way, with the other parts of the world just being a bit farther, but thats how i've always viewed it.

Just zooming out and simply seeing that small land mass below me is always great. As the level is an island in a sea in nothing, so is the earth in a sea of empty space, but outer space doesn't have a flat sky above it. I don't know, the sky/clouds really play a big role for me.

the fact that even if you fight of a hoard of viri they can easily come back so you can't just slowly dwindle enemys down you have use stratedy like (5squadsx 6 squadies x 4 bomers) 120 bombs then kill of your progrmas get some enginiers in and some turets and secure the island